Nutrient salts

Japanese: 栄養塩類 - えいようえんるい（英語表記）nutrient salts

Elements such as silicon, phosphorus, and nitrogen, which are essential for the formation of plants such as phytoplankton and seaweed, are dissolved in seawater mainly as silicates, phosphates, and nitrates, respectively. These inorganic salts are called nutrients. Nutrients act as fertilizer for the sea, nourishing phytoplankton, which feed on zooplankton, which in turn feed on fish, forming the basis of the food chain. After death, animals and plants decompose and dissolve into seawater as nutrients, which sink from the top to the bottom, making the deep sea a large reservoir of nutrients. In general, nutrients are more abundant in coastal waters and less abundant in open ocean waters. This is because land waters rich in nutrients flow into the coasts. However, even in the open ocean, upwelling currents exist in areas with raised seabeds such as reefs and seamounts, which carry nutrients from the deep sea to the upper layers, fertilizing the seawater and creating good fishing grounds. Large fishing grounds have also developed off the coasts of California and Peru as a result of coastal upwelling of seawater. Furthermore, vertical convection in seawater in winter also carries nutrients from the deep layers to the upper layers, so that in shallow seas or seas with weak density stratification, nutrients are relatively abundant in the upper layers. However, when nutrients become excessive, they cause a large proliferation of certain plankton, which leads to secondary pollution such as red tides. The main sources of nutrients in inland waters are wastewater from food industries, household wastewater, treated sewage water, and fertilizer spraying. Phosphates, a buffering agent, are also considered to be a problem in household neutral detergents. Both are difficult to remove using natural or biological treatment methods, so as a countermeasure, it is necessary to install purification facilities such as tertiary treatment in sewers. In addition, mandatory reductions in emissions from each source have been implemented (Seto Inland Sea), and they are also being considered as targets for total volume restrictions. (→Eutrophication)

Source: Encyclopaedia Britannica Concise Encyclopedia About Encyclopaedia Britannica Concise Encyclopedia Information

Japanese:

植物性プランクトンや海藻などの植物体をつくるのに不可欠なケイ素，リン，窒素などの元素は海水中でそれぞれおもにケイ酸塩，リン酸塩，硝酸塩として溶存している。これらの無機塩類を栄養塩類という。栄養塩は海の肥料の働きをし，植物プランクトンを養い，これを餌とする動物プランクトン，さらにそれを餌とする魚がふえるという食物連鎖の基本をなす。動植物は死後分解して栄養塩として海水に溶け込み，上層から下層へ沈降するため，深層は栄養塩類の大きな貯蔵庫となっている。一般に栄養塩は沿岸水に多く，外洋水に少い。これは栄養塩を多く含んだ陸水が沿岸に流入するためである。しかし外洋においても礁や海山など海底に隆起部のあるところでは湧昇流が存在し，これが深層の栄養塩を上層に運び海水の肥沃化をもたらし，よい漁場をつくる。またカリフォルニア沿岸や，ペルー沿岸においては海水の沿岸湧昇の結果，一大漁場が発達している。さらに冬季における海水の鉛直対流も深層から上層に栄養塩類を運ぶ働きをするので，浅い海や，密度成層の弱い海では栄養塩は上層で比較的豊富になる。しかし栄養塩類が過剰な状態になると，特定プランクトンを大増殖させ，赤潮など2次汚濁の原因になる。食品工業からの排水，家庭排水，下水道処理水，肥料散布などが陸水での主要な発生源である。家庭用中性洗剤も，緩衝剤のリン酸塩が問題とされている。いずれも自然，または生物的処理法では除去がむずかしく，対策として，下水道の3次処理など浄化施設の設置が必要である。また各発生源からの排出量削減義務づけなどが実施され (瀬戸内海) ，あるいは総量規制の対象としても検討されている。 (→富栄養化 ) 　

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